1. Field of the Invention
The invention relates to a windshield wiper system for vehicles with a windshield which is curved transversely, i.e. it is curved across its width. The system is provided with at least one driven wiper arm on whose free end a wiper blade is mounted. The wiper blade is caused to pivot about a longitudinal axis parallel to the wiper blade. A pivot drive for the wiper blade is derived from the wiper arm movement.
Particularly passenger vehicles have windshields with an arch across their width. The arch usually becomes steeper at the lateral regions. A wiper arm which only oscillates across the arched window therefore only has one position in which the wiper blade lies vertically on the window, while all other positions within the wiping area result in a deviation from the 90.degree. position. That deviation from the vertical, also called the normal error, influences the wiping quality, the reorientation characteristic of the wiper rubber in the reversal points and the aerodynamic properties of the wiper system.
2. Description of the Related Art
It has been attempted, therefore, to provide windshield wiper systems in which the wiper blade is pivoted in addition to the oscillatory motion. A windshield wiper of the above-mentioned type has become known from EP-A 351 528, for example, in which pivoting of the wiper blade on the wiper arm in dependence on the oscillation angle of the wiper arm is caused by a bendable shaft which is fixed at one end. While this leads to a change in the attack angle of the wiper blade, it does not consider the windshield curvature, however. The attack angle will remain approximately constant in this only in those special instances in which the windshield curvature follows the pivoting of the wiper blade on the wiper arm. This is generally not the case in the lateral edge regions, however, as can be seen in FIG. 2 of EP-A 351 528.
U.S. Pat. Nos. 3,006,788 and 2,979,425 show structures in which the wiper arm is formed of two parts and the part carrying the wiper blade is pivotable in a second part by means of a rod assembly which is slidable in a non-linear slaving guide.
In the windshield wiper according to U.S. Pat. No. 4,858,268, a pivoting of the wiper arm takes place in dependence on its oscillation about a transverse axis. Only a curvature of the windshield in a direction of the transverse axis is considered.
Finally, windshield wipers are known from EP-A 21 914 and 330 663, whose wiper arm or the wiper arm part carrying the wiper blade are pivoted about its longitudinal axis, whereby a control cam and a cam follower element are provided in the region of the wiper arm oscillation bearing. These two embodiments are able to keep the normal error at least small, as long as the wiper blade extends approximately parallel to the wiper arm. In reality, however, this parallelism is given only with few windshield wipers, since substantial angles are present between the wiper blade and the wiper arm in the parking position and for a best possible coverage of the driver's viewing field. Such configurations are particularly unsuited for windshield wiper systems, the wiper blade of which is guided across the windshield substantially parallel and which are rotated relative to the wiper arm for that purpose.